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(397) INCREASED CASEIN mRNA ABUNDANCE BY GROWTH HORMONE TREATMENT IN LACTATING MAMMARY TISSUE. Yang, Jinzeng 1, Zhao, Baoping1, Yanagimachi, Ryuzo 2, Kennelly, John3, 1 Dept of Human Nutrition, Food and Animal Sciences, Honolulu, HI2 Dept of Anatomy and Reroductive Biology, Honolulu, HI3 Dept of Agricultural, Food and Nutritional Sciences, Edmonton, AB, Canada ABSTRACT- In lactating cows, bovine growth hormone (bGH) administration not only increases milk production, but also can sustain milk systhesis for longer period of time. We observed that beta-casein mRNA abundance was significantly increased by two-month bGH infusion in lactating cows (P<0.05). To investigate whether the increased beta-casein mRNA resulted from bGH direct action on the mammary gland, explants made from mammary tissue of lactating rats and cows were incubated with bGH and prolactin supplementations. We further demonstrated that GH effected in a similar way as prolactin on beta-casein mRNA accumulation. The supplementation of either prolactin or bGH induced an elevated level of beta-casein mRNA accumulation over the controls: fresh tissue, and the explants incubated in basal medium containing insulin and hydrocortisone (P<0.05). In the explants from mammary tissue of the lactating cows having received twice daily milking and biopised at 6 hr after previous milking, levels of beta-casein mRNA were not increased by supplementation of GH or prolactin. In contrast, explants from the mammary tissue of the lactating cows having received once daily milking, and bipoisied at 20 hr after previous milking, showed an increased level of beta-casein mRNA by bGH supplementation, as well as prolactin. These results provide evidences that additional supply of bGH increases beta-casein mRNA abundance in lactating cows possibly through its direct action on the mammary gland. KEY WORDS: casein, growth hormone, lactation, mammary explant |
